On the positron annihilation spectroscopy and tensile behavior of COOH-MWCNT/epoxy nanocomposites

Positron Annihilation Lifetime Spectroscopy (PALS) is sensitive to the material voids/free volume on the atomic scale. For this reason, this method has been used as a unique technology to measure the free volume and structural defects in polymers in recent years. In the present study,  epoxy-matrix nanocomposites with different carboxylic acid functionalized multiwalled carbon nanotubes (COOH-MWCNTs) loadings (0.1-0.7 wt% at a step of 0.2) were fabricated, and the influence of COOH-MWCNTs loading on the prepared nanocomposites’ free volume properties and tensile behavior were explored. The measurement of positron annihilation lifetime was done using a conventional synchronization system based on a 22Na radioactive source with 7 μCi activity. The detectors used in this work were fast plastic scintillators (type: NT-850) with ns time response. The results demonstrated that the tensile strength of the nanocomposites decreased with the increase in the lifetime of the ortho-positronium annihilation (increase in the radius and free volume) in the samples. The 0.3 wt% COOH-MWCNTs/epoxy nanocomposite showed the maximum tensile strength. Overall, the results of this work clearly revealed that there was a strong relationship between the tensile strength and free volume in the polymer nanocomposites.